My invention relates to vacuum lifters of the general type disclosed for example in U.S. Pat. Nos. 1,426,930 (Waldron), 3,154,306 (Elliott et al.), and more particularly to U.S. Pat. No. 3,863,969 (Weiss et al.).
Previously known vacuum lifters employ a flexible cup formed of rubber or a rubber-containing composition to engage the surface of a load to be lifted. Suction is applied to the hollow interior of the cup in the conventional manner to adhere the lip or rim of the cup to the load surface by vacuum so that the load can be lifted and transported from one location to another. However, rubber and compositions or material containing rubber are not suitable for handling metal sheets or parts that are heated to high temperatures, for example sheet metal parts that are heat-treated or hot-formed in furnaces or ovens.
To overcome the inability of rubber or rubber-like materials to withstand high temperatures, Weiss et al. (No. 3,863,969), cited above, propose to employ, in a vacuum lifter, a sealing ring made of rubber-bonded asbestos fibers, which ring engages the surface of hot sheet metal, as described under "Example", Columns 4 and 5. By means of the sealing ring, and the use of certain specified lubricants in conjunction therewith, metal sheets heated to temperatures ranging up to 1000.degree. F can be handled.
A primary disadvantage in the Weiss et al. lifter is described in Column 5, lines 59-64, (U.S. Pat. No. 3,863,969) wherein it is stated that some of the sealing ring binder burns out under exposure to temperatures between 900.degree. and 1000.degree. F. It can thus be inferred that the sealing ring must be replaced from time to time.
Another disadvantage in the Weiss et al lifter is the relatively complex arrangement of metal rings, angular relationships between components, C-washers, and the assembly of spring loaded pressure pins required to force the sealing ring into engagement with the surface of the load to be lifted.
It is an object of my invention to provide a vacuum lifter that is relatively simple and inexpensive to manufacture, which can be used to handle formed metal parts or pieces that are heated to temperatures of 400.degree. F, and higher.
It is another object of my invention to provide a vacuum lifter in which the vacuum seal member is highly resistant to heat and wear.
Other advantages inherent in the vacuum lifter herein disclosed will clearly be seen in the ensuing detailed specification and drawings.